Acetabular dysplasia may be the leading cause of premature osteoarthritis (OA) of the hip. However, the relationship between the altered geometry associated with dysplasia and the resulting stresses in and around the joint is poorly understood. The overall hypothesis of this study is that acetabular dysplasia causes alterations in hip joint biomechanics, which predispose the joint to cartilage degeneration. Subject-specific, three-dimensional finite element modeling techniques will be developed and validated to study hip joint biomechanics. Then, using three patient populations (normal, traditional dysplastic and retroverted dysplastic), patient-specific finite element models will be used to determine stresses in and around the hip joint during simulated walking, stair-climbing and descending stairs. Patient-specific hip joint computational models also have a number of potential longer-term uses and benefits, including patient-specific approaches to treatment, and prediction of the long-term success rate of corrective surgeries based on pre- and post-operative mechanics. The methods to be developed and validated in this research can be directly applied to quantify changes in mechanical loading due to surgical intervention, allowing us to assess the efficacy of different approaches to osteotomy on a patient-specific basis. We also envision using these techniques for longer-term prospective studies, to correlate surgical correction with changes in mechanical loading and long-term outcome. Currently, the status quo is that long-term success is measured by avoidance of a total hip arthroplasty and is not correlated with any preoperative variable other than the relatively crude measurements made on an anteroposterior radiograph. Relevance to Public Health: Many orthopaedic surgeons are unaware of multiple facets of the hip dysplasia diagnosis and their potential implications for joint degeneration. Recognizing the mechanical consequences of different and often subtle forms of dysplasia allows earlier identification of "at risk'hips so that earlier treatment can be initiated, hopefully delaying the need for total hip athroplasty. This research will immediately help to delineate the true spectrum of this three-dimensional pathology by quantifying stress transfer in the hip joint using patient specific computational models.